NUSA DUA, Indonesia (Reuters) - Millions more people will be at risk from illnesses such as malaria and diarrhea in a warming world beset by heatwaves and water shortages, the World Health Organization said on Thursday.

Climate experts say rising temperatures and heatwaves will increase the number of heat-related deaths, while higher ozone levels from pollution will mean more people suffering from cardio-respiratory disease.

A warming world would also mean the spread of vector-borne and pathogenic diseases such as malaria, dengue fever and cholera.

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"Some of the major killers are climate sensitive," Maria Neira, the World Health Organization's director for public health and the environment, said at climate talks in Bali.

"We are concerned about malnutrition related to lack of agricultural production, we are concerned about diarrhea due to water scarcity and sanitation, and about seeing an increase in dengue and malaria and their appearance in areas where it was not present," she said.

"The health costs of inaction will be the incidence of injuries and death by natural disasters and heat waves or displacement of people."

Neira told the climate talks on the Indonesian resort island of Bali a 1 degree Celsius increase in temperature would lead to an 8 percent increase in the incidence of diarrhea.

Climate change was also expected to increase the proportion of the global population exposed to dengue, a disease carried by mosquitoes, by between 50 and 60 percent.

The 190-nation U.N. climate meeting in Bali from Dec 3-14 is seeking to launch two years of formal negotiations meant to end with agreement on a broad new U.N. pact to fight global warming, which is linked with rising sea levels, floods and melting glaciers.